This invention relates to reactors in petroleum refineries and, more particularly, to bubble caps for use in reactors.
In ebullated (expanded) bed reactors, hundreds of bubble caps are used to help provide for uniform flow distribution of the oil feed. Conventional bubble caps are keyed to risers and tack welded or back welded to cap screws. Periodically, the reactors must be shut down for maintenance and removal of coke buildup.
In order to disassemble or remove conventional bubble caps for maintenance and decoking, it is usually necessary to grind the welds off the cap screws or, alternatively, remove the cap screws with an impact wrench. Such grinding is very tedious, time consuming, and expensive, particularly since the reactors contain hundreds, and sometimes thousands, of bubble caps. Impact wrenches often create severe torques which can shear the keys and damage the bubble caps. After the bubble caps are decoked and their associated check valves are cleaned or replaced, the sheared keys must be repaired or replaced. Such repair and replacement are very cumbersome, laborious, and expensive. It also requires rewelding, such as Heliarc welding with a tungsten inert gas, which may not be effective if there is not enough weld metal to secure and rebuild the keys. Once the keys are restored, rebuilt, and repaired, the cap screws must again be back welded to the bubble caps. This procedure greatly increases the downtime of the reactor and the expense of maintenance and decreases the profitability of the refinery.
Furthermore, occasionally during operation of the unit, the back welds of the cap screws will break and the cap screws will unscrew. This can lead to additional shutdown of the reactor, which is very expensive and undesirable.
Over the years, a variety of lock washers, lock nuts, and other locking devices have been developed. Typifying these prior-art lock washers, lock nuts, and other locking devices are those found in U.S. Pat. Nos. 57,132, 76,201, 257,778, 257,788, 281,344, 394,537, 396,691, 405,632, 494,338, 514,397, 527,179, 549,529, 608,162, 613,630, 626,271, 753,415, 858,549, 860,758, 873,424, 923,264, 929,827, 950,123, 950,282, 968,991, 970,274, 982,763, 1,033,759, 1,041,832, 1,077,080, 1,089,175, 1,130,851, 1,202,893, 1,208,620, 1,235,717, 1,287,371, 1,288,482, 1,308,505, 1,333,529, 1,378,116, 1,382,306, 1,578,160, 1,598,165, 1,617,914, 1,634,744, 1,707,931, 1,733,529, 1,816,192, 1,881,935, 1,896,650, 1,898,801, 1,934,972, 1,951,228, 1,552,681, 2,031,530, 2,290,056, 2,374,403, 2,384,668, 2,950,944, 3,318,355, 3,421,563, and 4,286,807. These prior-art lock washers, lock nuts, and locking devices have met with varying degrees of success. None of these lock washers, lock nuts, and locking devices, however, have been used with bubble caps.
It is, therefore, desirable to provide an improved bubble cap assembly which overcomes most, if not all, of the preceding problems.